They were kind of odd, as I remember. Never read the Mankind comics, but I got a glimps of the Undertaker's. He was like a bounty hunter for the devil, hunting down demons and sending them back to hell. Usually by fighting them in the Squared Circle and letting them have a Tombstone Piledriver for their penance. Paul Bearer was his nemesis for what I saw, with Kane being his muscle/right-hand man.

I don't know what, but I'm guessing Mankind's plot had some kind of crazy going on with it too, I'd even say I think I remember the two comics crossing over at one point, with Mankind working for Bearer to get revenge on the Undertaker for past transgressions.

I still have some Undertaker comics. He was the boss man of the Stygian abyss, hell's prison. Until Paul Bearer some how stole his powers and chucked him into a human form with parents and a lil bro (IE Kane). Lil'Taker then burns down his house and parents. And somehow Kane lives but with fire powers and a fubared face. Another part of the concept is that half the WWE's roster is demonicaly possesed humans. Which crazy-ass Mankind can see for some reason. And taker does send the demons back home with his tombstone piledriver.

It was fairly weak plotting. Even for a comic.

There is also a Steve Austin comic. Where he drives around in a pick-up with his trademark leather vest sans shirt. Drinking beer and beating the piss outta people.